In the past, the air bubble-containing soap, whose specific gravity is decreased by introducing air bubbles etc. so that it can float on water, has been publicly known.
On the other hand, the soap preparation methods are broadly classified into the framing method and the milling method.
The framed soap is prepared by pumping molten soap at a high temperature into a cylindrical cooling frame, cooling/solidifying the soap together with the cylindrical cooling frame, and then cutting and forming.
On the other hand, in the case of milled soap, soap chips that are formed beforehand are kneaded and plodded to shape a bar soap.
Among these common soap production methods, it has been very difficult to produce an air bubble-containing soap especially by the framing method.
That is, in the framing method, high-temperature/low-viscosity molten soap is pumped into a cylindrical cooling frame. Therefore, even when air bubbles are entrained in the molten soap, air bubbles float and separate inside the cylindrical frame during the cooling process. By cutting and shaping after cooling, a soap containing a large amount of air bubbles and a soap containing a very small amount of air bubbles are generated. Thus, it is difficult to obtain an air bubble-containing soap of uniform quality.
Therefore, in order to produce an air bubble-containing soap, the milling method was used in the past (patent literature 1). Alternatively, air bubbles were entrained in molten soap by individual shaping (method in which molten soap is poured into a frame of one soap, patent literature 2 etc.). Thus, either of these production methods has been used.
Patent literature 1: Japanese publication of examined application No. S59-27796
Patent literature 2: Japanese unexamined patent publication No. 2006-176646